The first key telephone system (KTS), the 1A was a hardwired system comprising components physically wired together by hand. Developed by the Bell System and first marketed in 1938, the 1A was an electromechanical system. See also 1A1, 1A2, and KTS.
"1A." YourDictionary, n.d. Web. 15 May 2018. <http://www.yourdictionary.com/1A>.
1A. (n.d.). Retrieved May 15th, 2018, from http://www.yourdictionary.com/1A